Tennis player Donald Young has made an allegation of racial prejudice against fellow American Ryan Harrison, saying he was "shocked and disappointed" by remarks during a heated exchange at the New York Open, which Harrison has said is "untrue."

In Serena Williams' first competition since giving birth five months ago, she and her sister Venus Williams lost 6-2, 6-3 to Lesley Kerkhove and Demi Schuurs of the Netherlands on Sunday in a Fed Cup doubles match.

The Czech Republic advanced to the Fed Cup semifinals after two-time Wimbledon champion Petra Kvitova beat Switzerland's Belinda Bencic, while France and Germany moved on with wins in deciding doubles matches.

The top-seeded Federer needs to reach the semi-finals to return to the top spot for the first time since 4 November 2012. But the 36-year-old Swiss might have to beat his surging countryman Stan Wawrinka in the quarter-finals.

Wawrinka is the fifth seed at the ATP World Tour 500 event, and appears to be well on his way to regaining top form. Wawrinka is in the semi-finals this week at the Diema Xtra Sofia Open in Bulgaria. Federer will face a qualifier in the first round and will meet either German Philipp Kohlschreiber or Russian Karen Khachanov in round two.

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Federer first rose to the top spot 14 years ago on 2 February 2004 and holds the record for most weeks spent at No. 1 (302). If he makes the semi-finals, he will become the oldest No. 1, eclipsing Andre Agassi (33).

Federer moved to within 155 points of World No. 1 Rafael Nadal after claiming his 20th Grand Slam title at the Australian Open last month. The Swiss right-hander has previously played the ATP World Tour 500 tournament in Rotterdam eight times, taking the title in 2005 and 2012.

* Nadal is guaranteed to stay No. 1 until at least 18 February 2018.
^ Federer is 36 years old as of 19 February 2018.

Nadal, who is not scheduled to play again until Acapulco in the last week of February, has held No. 1 for the past 25 weeks (since 21 August 2017). The Spaniard has been No. 1 in the ATP Rankings a total of 166 weeks since first taking over on 18 August 2008. Nadal is seventh all-time in most weeks at No. 1 in the history of the ATP Rankings (since 1973).

First and Last Day at No. 1

PlayerDebut at No. 1Most Recent Date at No. 1Time In BetweenRafael Nadal*
18 August 2008
18 February 2018
Nine years, 184 days
Jimmy Connors
29 July 1974
3 July 1983
Eight years, 339 days
Roger Federer^
2 February 2004
4 November 2012
Eight years, 276 days
Andre Agassi
10 April 1995
7 September 2003
Eight years, 150 days
Pete Sampras
12 April 1993
19 November 2000
Seven years, 221 days

* Nadal is guaranteed to stay No. 1 until at least 18 February 2018.^ 19 February 2018 marks 14 years, 17 days since Federer debuted at No. 1 on 2 February 2004.

Federer has a 23-6 record in Rotterdam. In addition to his two titles, he reached the final in 2001 and semi-finals in 2003. His last appearance at the Rotterdam Ahoy stadium in The Netherlands was 2013, when he lost in the quarter-finals to Julien Benneteau.

Longest Gap Between Stints at No. 1

PlayerLost No. 1Regained No. 1Time In BetweenAndre Agassi
12 February 1996
5 July 1999
Three years, 142 days
Jimmy Connors
9 July 1979
13 September 1982
Three years, 65 days
Rafael Nadal
6 July 2014
21 August 2017
Three years, 45 days
Andre Agassi
11 September 2000
28 April 2003
Two years, 228 days

* February 19, 2018 marks five years, 106 days since Federer was last No. 1 on 4 November 2012.

Should Federer make the semi-finals, his path hardly gets easier. Alexander Zverev could await in the last four, and on the opposite side of the draw, fourth seed David Goffin, who beat Federer at the 2017 Nitto ATP Finals, lurks along with World No. 4 Grigor Dimitrov, the second seed at the ATP World Tour 500 event.

One year ago this week, David Goffin made his first big run of what would turn out to be many in a career campaign when he advanced to the final in Sofia (l. to Dimitrov). This year, the Belgian is in a different location, Montpellier, but the result looks much the same.

The first Belgian to qualify for the Nitto ATP Finals (2017) will face three-time Montpellier champion Richard Gasquet, who extended his record at the event to 21-2 since 2013 by beating fourth seed Damir Dzumhur 6-4, 6-2.

The home favourite was 1-4 down against the Bosnian in the opening set before storming back to win 11 of the final 13 games in the pair's first FedEx ATP Head2Head matchup. The 31-year-old broke his opponent five times in the match, winning 68 per cent of second-serve return points.

Gasquet will attempt to advance to the Open Sud de France final for the sixth year in a row. He lost his only previous FedEx ATP Head2Head meeting against Goffin in Tokyo last year. The Frenchman has not won a title since 2016 Antwerp.

Third seed Jo-Wilfried Tsonga will hope that the third time is the charm after he beat #NextGenATP Russian Andrey Rublev 6-4, 7-6(1) to advance to his third semi-final in Montpellier (2010, 2017). He is in pursuit of his fourth ATP World Tour indoor title since the beginning of last season.

Tsonga's quarter-final victory was simpler than his opening-round match against Nicolas Mahut, in which he was pushed to three tie-breaks. The World No. 19 saved four of five break points and won 60 per cent of second-serve return points to triumph against Rublev, the World No. 36.

The dynamic Frenchman, who fell 4-6 in the third set at both previous semi-final opportunities in front of his home crowd, will play second seed Lucas Pouille, who ousted compatriot Benoit Paire 6-1, 6-4 in 54 minutes.

The top-ranked Frenchman (World No. 17) has captured one ATP World Tour title in France (2016 Metz) and reached one final in his home country (2017 Marseille).

Tsonga leads the pair's FedEx ATP Head2Head series 2-1, but Pouille won their last meeting in the Vienna final last year.

DID YOU KNOW?Goffin did not win a match in Montpellier before this week. The World No. 7 fell in qualifying in both 2010 and 2012.

The Swiss extended his FedEx ATP Head2Head series lead against the Serbian to 9-0, with their most recent match coming in the third round of the 2017 Australian Open. Wawrinka, who is still on the mend after two left knee surgeries last summer, is into the 57th tour-level semi-final of his career (28-28).

After getting pushed to three sets in his opening-round match, Wawrinka appeared in control of his quarter-final. The World No. 15 surged through the opening set, losing just five points on his serve. But in the second set, Troicki found his game and broke the Swiss for a 5-3 lead. And while he could not serve out the set, Troicki also held a 3/0 lead in the ensuing tie-break. Wawrinka was too strong on the day, though.

"I'm doing everything to keep winning, that's for sure," Wawrinka said. "I'm enjoying my time, I'm fighting on the court and that's the most important."

The 32-year-old will next play qualifier Mirza Basic. The Bosnian is into his second ATP World Tour semi-final after dispatching German Maximilian Marterer 6-4, 4-6, 6-3.

Basic has now advanced to the semi-finals at two of his past three ATP World Tour 250 events, with the previous appearance coming in Moscow, where he lost to compatriot Damir Dzumhur.

In the bottom half of the draw, Romania’s Marius Copil advanced to the first ATP World Tour semi-final of his career by remaining composed in a 6-4, 6-4 victory over third seed Gilles Muller of Luxembourg. One break in the ninth game of each set proved to be enough for Copil, who struck 13 aces and lost eight of his first-service points in the 80-minute encounter. He’d previously lost five quarter-finals and now faces Slovakian qualifier Jozef Kovalik.

Kovalik, who saved one match point in beating countryman Lukas Lacko in the second round, defeated Cypriot Marcos Baghdatis 7-6(2), 6-4 in one hour and 53 minutes.

“I feel amazing and I enjoyed the match today, it was a nice atmosphere,” Kovalik told ATPWorldTour.com. “He is a great mover on the court, has good defence, a very good forehand and serve. I tried to push him and striker winners. Copil will be a different player, very aggressive, but it’s a good chance for both of us to reach our first final.”

Thursday was a dangerous day to be a seeded player at the Ecuador Open.

Four seeds, including the only champion the tournament has ever had, all fell in a wild day of tennis in Quito. Three-time champion Victor Estrella Burgos was the first to fall. The Dominican had been 16-0 in Quito, by far his favourite place to play.

“I want to congratulate my opponent, he played a good match... He attacked well with his crosscourt forehand,” Estrella Burgos said. “I have won three times here. I would be arrogant saying I’m sad today. How many players would like to have three ATP titles? I hope to be back next year.”

Melzer said: “He won 16 matches in a row here and the previous times we played, we always had a battle. I knew it was going to be a very tough match, and I knew I had to play very well to beat him here.”

Melzer will next meet Spaniard Albert Ramos-Vinolas, who was one of only three seeded players to advance to the quarter-finals. The second seed toppled Ecuador's No. 1 Roberto Quiroz 6-3, 3-6, 6-3.

Third seed Gael Monfils, playing in his first ATP World Tour match in South America, also needed three sets to move into the quarter-finals. The Frenchman beat #NextGenATP Casper Ruud of Norway 6-3, 3-6, 6-4. Monfils is looking to celebrate his second title of the season after winning the Qatar ExxonMobil Open in Doha during week one.

“I think Casper is a very talented guy... I'm very happy to come through,” Monfils said.

But no other singles seeds who were in action on Thursday found themselves still on the Quito draw sheet at the end of play. Top seed Pablo Carreno Busta, World No. 10, fell to No. 156 Andrej Martin of Slovakia 6-4, 6-2 in just 65 minutes. It was Martin's first Top 10 win (1-2).

“The biggest key for me was I had already played two matches here, this was my third match, so I was already used to these conditions,” said Martin, who qualified for the ATP World Tour 250, “and also I really like these conditions here.”

The third seed never broke countryman Nicolas Mahut, but Tsonga still prevailed past the serve-and-volleying Mahut 7-6(3), 6-7(3), 7-6(4). Tsonga saved three break points, and Mahut saved four in the second-round match that lasted two hours and 24 minutes.

Tsonga has made the semi-finals both times he’s played Montpellier, 2010 and 2017, and in the quarter-finals, he'll meet #NextGenATP Russian Andrey Rublev.

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Three other Frenchmen also advanced, including second seed Lucas Pouille, who dropped only one point on his first serve (22/23) to breeze past #NextGenATP Spaniard Carlos Taberner 6-1, 6-2.

Three-time champion Richard Gasquet made another Montpellier quarter-final, toughing out a three-setter against countryman Pierre-Hugues Herbert 7-6(3), 5-7, 6-3. In the decider, Gasquet converted his lone break point and didn't let Herbert see such an opportunity. Benoit Paire, 2013 finalist (l. to Gasquet), hit 17 aces to knock out Aussie John Millman 6-4, 7-6(4).

Klizan pressed the action early and claimed the first set in 37 minutes, but Wawrinka settled down and battled back, managing to break Klizan in the fourth game of the second set. His confidence restored, Wawrinka broke again at 5-2 to close out the set.

"I expected a tough match; he's already played a few matches here," Wawrinka said of Klizan, who qualified for the event. "I just tried to focus on my game, find the right shots and be aggressive."

The top-seeded Wawrinka was playing in his first match since a second-round loss at the Australian Open last month, and just his third match since Wimbledon last year (knee injury). Wawrinka will face Viktor Troicki in the next round. Troicki, a finalist in Sofia in 2016, was also pushed to three sets before overcoming Denis Istomin, 7-6(4), 1-6, 7-6(5).

"I know Viktor is playing really well here and I'm expecting a tough match; I'm going to try and rest now to be ready for tomorrow," Wawrinka said.